1. Field of the Invention
The present invention relates to a method for modeling a defect management routine in a manufacturing process and for handling the defect during the production process based the defect management routine.
As it is well known, the art according to the ISA S-95 standard, a method for managing and controlling manufacturing processes planned by an Enterprise Resource Planning (ERP) and produced by a shop floor, provides a manufacturing executing system (MES) for implementing the planned manufacturing processes and controlling the corresponding production steps at shop floor.
In particular, the Enterprise Resource Planning (ERP) is a system including hardware devices and corresponding software applications for planning the business resources of an enterprise, i.e. material provisions, human resource management, purchasing, orders, profits, finance, inventory controls, customer management, etceteras, while the term “shop floor” has been used to indicate a system supporting the control of single machines involved in the manufacturing processes, for example by measuring the number of pieces produced per hour by each machine or the functioning parameters thereof, the quality of the pieces produced and so on.
As schematically represented in FIG. 1, MES is an intermediate layer providing computing machines and software tools 1-n between the ERP upper layer and the shop floor lower layer, including a software tool for production order management 1, which receives requests of production from the ERP, and a software tool for production modeling 2, which supports the engineering phases of selecting and managing the resources to be involved in the manufacturing processes, i.e. employees, machines and materials, in order to realize a planned manufacturing process within required time constrains.
MES is based on the International Standard Association (ISA) standard S95 which defines how software tools 1-n may implement the production at shop floor level and how communicating with it. More particularly, as represented in FIG. 2, S95 is substantially based on a manufacturing process represented by a plurality of sequential process segments PS1, PS2, PS3, PS4 wherein each sequential process segment contains a plurality of actions A1, An to be performed sequentially at the shop floor level.
An execution of the MES software tool described above includes the management of the manufacturing process by activating a sequential process segment PS1 and sequentially executing the corresponding plurality of actions A1, An.
More particularly, in order to complete a manufacturing process, the software tool for production order management 1 substantially repeats the steps of activating and waiting the end of a plurality of sequential process segments, for a plurality of process segments. In this case, a plurality of software tools, corresponding to respective sequential process segments, is executed for the duration of the corresponding sequential process segment.
Advantageously, MES supports very well the manufacturing processes including sequential process segments which may be executed synchronously and continuously, for example in industrial production processes or batch industries which are implemented by well described algorithms or sequential steps, as it is for instance, in a food producing process of the type involving the following steps “fill mixer with material 1”, “fill mixer with material 2”, “mix material for 10 minutes”, and “discharge”, wherein the material 1, material 2 as well as the mixer are available.
However, MES does not support as well manufacturing processes including some processes which may be stopped for long periods, for example due to the lack of a resource, machine, material or personnel required to perform it. This occurs especially in discrete manufacturing processes, for example in automotive factories, as schematically represented in FIG. 2.
In this figure, the manufacturing process of assembling a car engine with the external structure of the car is schematically represented with a sequence of four sequential process segments wherein the first segment PS1 provides the engine assembling, the second segment PS2 the external structure assembling, the third segment PS3 the coloring of the external structure already assembled and the last segment PS4 the mounting of the assembled engine with the external structure already colored.
Each sequential process segment PS1-P4 contains a plurality of actions A1, A2, A3, A4, A5, An which are executed sequentially, i.e. action An cannot be executed until all the previous actions are terminated.
In this case, a first software tool for production order managing 1 is executed for activating the first action of segment PS1 and it remains in execution until the last action An of the process segment PS1 is ended, even if one action A3 is suspended for a long period. For example, even if some pieces of the engine are not available, because not already ordered or delivered to the plant floor, the software tool corresponding to the first segment PS1 is executed. A second software tool is executed for activating the first action A1 of process segment PS2 and it remains in execution until the last action An of the process segment PS2 is ended. In the same way, a third and a fourth software tools are executed for activating the first actions A1 of the corresponding sequential process segments PS3 and PS4 and waiting the end of their execution.
Also the second, third and fourth software tools are executed when some actions of the corresponding sequential process segments PS2, PS3, PS4 are suspended, for example because a door to be assembled in process segment PS2 is not already available and a color to be used in process segment PS3 has been used up.
This involves a great overcharge of computing machines executing the software tools, as well as a great number of computing machines involved in executing such software tool, especially when the manufacturing process is implemented by a high number of sequential process segments.
In other words, sequential process segments as defined above apply very well in industrial production processes and in general where process segment executions actually manage action which are continuously executed, so that the process segment execution cost is largely paid by a process control benefit.
However, it does not apply in discrete manufacturing processing, wherein there is no real process control continuously running during a complete life cycle of some products but a plurality of commands should be sent to machines at the plant floor level for producing a lot of products which are then moved to other machines. Moreover, in discrete manufacturing processing, many of the commands are issued manually by personnel, rather than automatically with predetermined order by an on top controller.
Further, defect identification and individuation as well as tracing of performed remedial action are generally a substantial topic within the MES application. Unfortunately, up to now the model according to the S-95 standard does not at all reflect these general requirements which consists for example in the need to catalog defects and give the users the opportunity to handle defects/anomalies in the production process also within the usually complex environment of a production plant. Further, the S-95 standard is currently completely silent about the tracing of extra work being performed on secondary lines in order to recover rejected products/pieces coming out of the production process.